Cancer remains one of the leading causes of death among humans worldwide. Current treatment methods often involve chemotherapy, surgery and/or radiation therapy. These mechanisms, while effective in short term treatment, are often accompanied by harsh side effects and offer little guarantee of preventing future relapses. In light of these problems, other long-term strategies for treating cancer have been researched.
One such strategy involves the use of exogenous mechanisms to stimulate a patient's immune system to target the aberrant cancer cells. Rosenberg, S. A. Nature. 411 380-384 (2001); Dudley, et al. Nat Rev Cancer. 3 666-675 (2003); Boon, et al. Annu Rev Immunol. 24 175-208 (2006). More specifically, tumor cells are understood in the art to display unique proteins on their cell surface that may act as antigens. Such antigens are most often comprised of epitopes or small peptide sequences within the antigen that, when recognized by the host's immune system, generate an immunological response. Such an immunological response occurs when the antigenic protein is engulfed and degraded within an antigen presenting cell through intracellular proteolytic breakdown. Peptide fragments, i.e. epitopes, are then associated with immunity stimulating molecules of the Major Histocompatibility Complex (MHC), often in the endoplasmic reticulum of the cell and transported to the cell surface for extracellular presentation and immunological stimulation. With respect to cancer cells, peptide antigens are often associated with class I MHC molecules and presented on the cell surface of the cancer cell.
The MHC class I molecule is a tetramer comprised of an alpha and a beta chain. The alpha chain has three polymorphic domains, α1, α2, α3 wherein the degraded antigen binds within clefts formed therebetween. Because one MHC molecule can bind numerous antigens, each molecule is named according to its locus within the Human Leukocyte Antigen (HLA) region of the genome. More specifically, HLA-A, HLA-B, and HLA-C each refer to different loci wherein superfamilies of Class I MHC molecules are encoded, and HLA-DP, HLA-DQ, and HLA-DR each refer to different loci where Class II MHC molecules are encoded. Once the appropriate MHC molecule is bound to the antigen and the complex is transported to the cell surface, the cell is then in a condition for recognition by, for example, a lymphocyte.
T lymphocytes (T cells), among many functions, recognize antigens or immunodominant epitopes that are associated with alleles of the human leukocyte antigens (HLA). There are at least two distinct types of T lymphocytes: CD4+ helper T lymphocytes (TH cells) and CD8+ cytotoxic T lymphocytes (CTLs). TH cells are involved in both humoral and cell-mediated forms of immune responses and typically, though not exclusively, recognize antigens in association with class II MHC molecules. CTLs, however, recognize and destroy cells which display foreign antigens on their surfaces wherein the antigens are typically associated with class I MHC molecules. The CTL's recognition of such foreign antigens occurs through a T cell receptor (TCR) located on the surface of the CTL.
A TCR is a immunoglobin protein that may be comprised of at least an alpha chain with a variable region and a constant region, a beta chain with a variable region and a constant region, and a transmembrane region. The variable region of the alpha chain may by comprised of at least three complementarity determining regions (cdr1, cdr2, and cdr3, respectively) and the variable region of the beta chain may be comprised of at least four complementarity determining regions (cdr1, cdr2, cdr3, and cdr4, respectively). While all three cdr regions of the alpha chain and all four cdr regions of the beta chain function to facilitate recognition of an antigen/MHC complex, the cdr3 is the most variable and plays a large role in determining which epitopes and antigen/MHC complex(s) the TCR will recognize Recognition of an antigen/MHC complex by the TCR triggers a cascade of protein and cytokine interactions leading to, among other interactions, the activation, maturation and proliferation of the precursor CTLs and resulting in CTL clones capable of destroying the cells exhibiting the antigens recognized as foreign.
Paraneoplastic neurologic disorders (PND) are autoimmune disorders caused by an onconeural antigen eliciting such a CTL mediated response. More specifically, cerebellar degeneration-related 2 protein (cdr2 protein) is one such onconeural protein normally expressed within immunoprivileged sites of the cerebellar Purkinje neurons in the brain, some brainstem neurons, and spermatogonia. Corradi, et al. J Neurosci. 17 1406-1415 (1997). However, research into paraneoplastic cereballar degeneration (PCD), a PND disorder wherein the patient's immune system destroys Purkinje neurons in the cerebellar cortex of the brain, revealed that the cdr2 protein is not limited to these cell types and may also be found within some gynecological tumor cells. (FIG. 1 in Corradi, et al. J Neurosci. 17 1406-1415 (1997)). Current research further suggests that the autoimmune effects of PCD are actually caused by cdr2-specific CTLs stimulated by the cdr2-expressing gynecologic carcinomas. Albert, et al. Nat Med. 4 1321-1324 (1998). In other words, cdr2-specific CTLs within the PCD patient, while competent to elicit an immunological response to the cdr2 expressing tumor cells, secondarily recognize and elicit an autoimmune response to the cdr2 expressing Purkinje cells. Accordingly, the epitopes of the cdr2 proteins are, in fact, onconeural antigens in that they signal the presence of a carcinoma, but also elicit an autoimmune response to neural cells.
Another such onconeural antigen is an antigen of the Hu protein family. The Hu protein family, also normally expressed exclusively in neurons, has been linked as a intracellular antigen associated with small cell lung cancers (SCLC). Darnell, et al. J Neurosci. 11 1224-1230, Darnell, et al. Proc Natl Acad Sci USA 93 4529-4536. It is believed that HuD expression by tumor cells exposes the antigen to the immune system, generating an HuD-specific and CTL driven immune response. This results in appropriate and partially effective tumor immunity against the SCLC. Darnell et al. N Engl J Med. 349 1543-1554, Darnell et al. Semin Oncol 33170-298. However, many Hu patients typically first present to clinicians with neurological symptoms triggered when this CTL driven tumor immune response, by unknown means, becomes competent to attack the nervous system, i.e. HuD expressing neurons.
There are, however, large populations of individuals with similar onconeural antigen expressing tumors who do not develop a PND. Darnell et al. Cancer Res. 60 2136-2139 (2000), Dalmau et al. Ann Neurol 27 544-552. Such populations suggest that antigen directed immunotherapy may be possible without the risk of developing PND, but only if the appropriate epitopes can be established. In fact, ˜20% of SLCL patients develop immune responses to the Hu antigen that correlate with improved clinical outcome, in the absence any signs of neurologic PND symptoms Graus, F. et al. J. Clin. Oncol. 15, 2866-2872 (1997); Dalmau, J., Furneaux, H. M., Gralla, R. J., Kris, M. G. & Posner, J. B. Ann. Neurol. 27, 544-552 (1990). In particular, strategies that might target a peripheral tumor, but that are not able to either get across the blood-brain barrier or are otherwise incompetent to attack neurons, may target tumor cells without inducing autoimmune disease. However, exactly which onconeural antigens are optimally recognized by a CTL, and which corresponding TCRs are present on those T cells were previously unknown.
Based on the foregoing, there is a need in the art for compositions and methods providing therapeutic avenues of treatment for subjects suffering from onconeural antigen expressing tumors and/or a PND. The present invention addresses and meets this need by providing a series of HLA allele-specific, immunodominant peptides as disclosed that elicit an immune response to the carcinoma with little to no autoimmune side-effect. Moreover, this invention addresses these needs by identifying TCRs able to recognize these HLA-peptide complexes present on tumor cells, and demonstrates that they are sufficient to induce killing in an otherwise naïve CTL.